1. Field of the Invention
The present invention relates to a machine for polishing rice grains to remove bran from a surface of each rice grain.
2. Description of the Prior Art
For example, as disclosed in the Japanese Patent Publication No. 34-4765 (Patent No. 255684) to Satake, a conventional rice polishing machine comprises a frame, a shaft mounted on the frame for rotation about an axis extending generally horizontally, a polishing roll mounted on the shaft for rotation therewith, and a perforated cylindrical polishing member mounted on the frame in concentric relation to the shaft. The perforated cylindrical polishing member cooperates with the polishing roll to define a polishing chamber therebetween. Each of a pair of partition wall members extends in parallel to the shaft and has one longitudinal side edge sealingly engaging with an outer circumferential surface of the perforated cylindrical polishing member at a location above the shaft and the other longitudinal side edge fixed to the frame, to thereby divide the outer circumferential surface of the perforated cylindrical polishing member into an arcuate top surface section and the remaining arcuate surface section and to define substantially closed upper and lower spaces. The arcuate top surface section and the remaining arcuate surface section of the perforated cylindrical polishing member are exposed to the upper and lower spaces, respectively. A blower communicates with the upper space to discharge air therefrom.
When the shaft is rotated, the rice grains to be polished are supplied into the polishing chamber, and the polishing roll is rotated to polish the rice grains within the polishing chamber, to thereby remove bran from the surface of each rice grain. An air flow generated by the blower is introduced from the lower space into the polishing chamber through apertures in the remaining arcuate surface section of the perforated cylindrical polishing member, and, subsequently is introduced from the polishing chamber to the upper space through apertures in the arcuate top surface section of the perforated cylindrical polishing member, thereby discharging the removed bran from the polishing chamber.
In the above-described conventional rice polishing machine, the revolution of rice grains caused by the rotation of the polishing roll is prevented because of their own weight, and the rice grains tend to be collected in the lower portion of the polishing chamber, thereby increase the density of rice grains in the lower portion of the polishing chamber and decreasing the density of rice grains in the upper portion of the polishing chamber.
In the above-described Satake patent, the decrease in rice grain density in the upper portion of the polishing chamber is positively utilized to discharge the bran and heat generated by the polishing action in the lower portion of the polishing chamber through the upper portion of the polishing chamber in which the rice grain density is low, by means of air introduced into the polishing chamber from the lower space, thereby enhancing the bran removing efficiency and suppressing effectively the rise in temperature in the polishing chamber.
With the arrangement described above, however, it has been found that the rice grains in the polishing chamber tend to be stagnated in the lower portion of the polishing chamber and such stagnation adversely affects the polishing action. This causes the rice grain density in the lower portion of the polishing chamber to be considerably increased. The rice grains, having the considerably high density, stagnated in the lower portion of the polishing chamber are subjected to an excessive pressure from the polishing roll, so that a speed of rotation of each rice grain about its own axis is decreased. The reduction in the rotational speed of each rice grain about its own axis causes such a problem that an outer surface of each rice grain is abraded non-uniformly by the polishing roll. Also, since the rice grains stagnated in the lower portion of the polishing chamber are high in density, it is difficult for the air introduced from the lower space into the polishing chamber to pass through the stagnant rice grains, so that the performance of carrying away the removed bran to the outside of the polishing chamber is reduced. Furthermore, the high density rice grains stagnated in the lower portion of the polishing chamber is subjected to an excessive pressure from the polishing roll and is broken to produce broken or damaged rice grains. Moreover, the revolution speed of the rice grains is increased in the upper portion of the polishing chamber where the rice grain density is low, due to their own weight, so that the rice grains impinge against the rice grains stagnated in the lower portion of the polishing chamber, and against the wall of the perforated cylindrical polishing member, to cause the broken rice grains.